Codechange: Use consistent name for bay road stops

As of #10494, this is how we describe original dead-end road stops.

Codechange: Use IsValidCargoID/IsValidCargoType.

IsValidCargoType() is used only for unmapped IDs.

Fix: O(N^2) cost of Station::RecomputeCatchmentForAll

Station::RemoveFromAllNearbyLists does not need to be called when
all station nearby lists have been cleared and are being regenerated.

Codechange: Use std::vector for station speclist

This removes manual memory allocation, although we still manage the list
size in roughly the same way.

Fix #7847: Use ViewportSign coordinates for sign Kdtree coordinates (#7849)

Ensure the same coordinates are used for station/town/player signs regardless of how the landscape changes below it after the coordinates were first determined.

By keeping track of whether each ViewportSign is valid for Kdtree use (and only ever registering the viewport sign when the object is valid) a lot of code can be simplified and become more robust at the same time.

Feature: Industries with neutral stations (e.g. Oil Rig) only supply/accept cargo to/from their neutral station. (#7234)

This change is a controlled by a game setting, located under Environment ->
Industries which allows toggling the behaviour. It defaults to enabled.

"Company stations can serve industries with attached neutral stations"

When enabled, industries with attached neutral station (such as Oil Rigs) may
also be served by company-owned stations built nearby. This is the traditional
behaviour.

When disabled, these industries may only be served by their neutral station.
Any nearby company-owned stations won't be able to serve them, nor will the
neutral station serve anything else other than the industry.

(svn r19956) -Fix: close list of vehicles with given oil rig in orders when the oil rig is deleted
-Fix (r19952): close the list when it is not sticky

(svn r18726) -Fix [FS#3463]: with non-uniform industries the 'supplies' text when building a station could be incorrect (missing a cargo)
-Change [NoAI]: AITile::GetCargoProduction now returns the number of producers and not the number of tiles of producers.
-Fix [NoAI]: AITileList_IndustryProducing would omit some tiles for at which a station would get cargo.

(svn r17113) -Change [FS#265][FS#2094][FS#2589]: apply the subsidy when subsidy's destination is in station's catchment area and cargo packets originate from subsidy's source
-Change [FS#1134]: subsidies aren't bound to stations after awarding anymore, they still apply to town or industry, no matter what station is used for loading and unloading. Awarded subsidies from older savegames are lost
-Change [NoAI]: due to these changes, AISubsidy::GetSource and AISubsidy::GetDestination now return STATION_INVALID for awarded subsidies